220 ReiJ. J. Bartoto^ [March 14, 



baked clay, or any other suitable material — the flux, &c., on one 

 side, and the metal on».the other.* 



In the experiment just described, the cryolite chiefly fulfils the 

 office of a flux. But, twelve mouths since, Dr. Percy obtained 

 aluminium directly from this mineral. f Cryolite is a fluoride of 

 aluminium and of sodium. Dr. Percy found that layers of tliis 

 substance, minutely pulverized, and heated with sodium in the 

 manner described in the last experiment, yielded aluminium. Cry- 

 olite is found only in Greenland. A geological diagram of its 

 locality, as well as some interesting specimens of the mineral itself, 

 were exhibited by Mr. J. W. Tayler.| 



Such being the present known methods of producing this re- 

 markable metal, the speaker adverted — 



2nd. To the pro])€rties of Aluminium. Its physical properties 

 are very characteristic. Its specific gravity (2'2o)§ is nearly that 

 of glass, and consequently below that of any metal (with the excep- 

 tion of the alkaline metals, and the metals of the alkaline earths). 

 It is malleable, ductile, and sonorous. Its fusing point is between 

 that of silver and zinc ; it resembles silver in its excellence as a 

 conductor of electricity. Lastly, it has great capacity for heat — 

 (about six times that of silver). But the chemical properties of 

 this metal are such as could not have been conceived until ascer- 

 tained by experiment. Instead of reassuming oxygen (like the 

 alkaline or earthy metals) with an energy proportioned to its ex- 

 treme tenacity of that element while in the state of oxide, aluminium 

 appears to be as indifferent to oxygen as gold or platinum are. It 

 is not affected by sulphur, like silver ; nor is it acted on (except to 

 a very slight degree) by any of the oxy-acids in the cold, its only 

 solvent being hydrochloric acid. The strong affinity between this 

 metal and oxygen before its separation, contrasted with the appa- 

 rently total indifference afterwards, suggests the possibility that at 

 the instant of its coming in contact with air, aluminium may receive 

 a fine coating of oxide — a film of transparent sapphire — from the 

 atmosphere, which protects it against the above-named corroding 

 substances. 



This conjecture is rendered plausible by the result obtained on 

 exposing a leaf of aluminium to the oxidizing flame of the blowpipe. 

 The result of the combustion, though apparently a mass of alumina, 



♦ As time and space for fire operations in the theatre were limited, this 

 experiment was not attempted during the discourse. But at an earlier period 

 of the day, M. Sainte-Claire Deville had the honour of performing it, in the 

 presence of H.R.H. Prince Albert, in the Laboratory of the Institution. 



t Proceedings of the Royal Institution, Vol. ii. March 30, 1855, p. 79 ; Phil. 

 Mag. Ser. 4, Vol. x. pp. 233 and 364 ; Comptes Rendus, Dec. 10, 1855, p. 1054. 



X Lit. Gazette, No. 2039, p. 109. 



§ The low specific gravity of aluminium, being nearly that of the flux em- 

 ployed in fusing it, enhances materially the difficulty of its production. M. 

 Deville, however, melted together some pieces of pure aluminium without flux, 

 and cast the fused mass in an ingot-mould before the audience. 



